Conventionally, electric vehicles (EV), which are mobile objects, are equipped with multiple motors, and as a means of distributing torque that drives the drive wheels (wheels), the following technologies have been disclosed.
A first technology distributes torque by calculating power consumption with respect to combinations of motor torque and by obtaining a graph that plots driving force distribution along the horizontal axis. In this configuration, magnitude relations of the power Pout [kW] that can be output and the smallest value of power consumption (hereinafter, lowest power consumption) when a motor torque combination realizing a transient, required driving force that is within a torque restriction is realized are compared. If the power Pout [kW] that can be output is judged to be greater than or equal to the lowest power consumption, the motor torque of the front-rear wheels that minimizes the power consumption is regarded to be the instructed torque as is (see, for example, Patent Document 1).
A second technology distributes total torque to multiple motors such that torque is distributed equally to the 2 front drive wheels and torque is distributed equally to the 2 rear drive wheels, by generating and using a system efficiency map indicating the torque distribution ratio that maximizes system efficiency (see, for example, Patent Document 2).
A third technology retrieves based on the required driving power and vehicle speed, a map indicating relations among fuel consumption, discharged and charged power of the electrical storage device, and front-rear wheel driving force distribution. From the extracted map, the driving force distribution that minimizes fuel consumption with respect to the discharged and charged power of the electrical storage device is extracted, whereby driving force distribution maps before and after improved fuel efficiency are obtained (see, for example, Patent Document 3).
In a fourth technology, based on vehicle speed and the required motor driving torque that corresponds to the required motor driving force and further based on the torque of each motor generator and efficiency characteristics corresponding to vehicle speed, a driving force distribution determining unit determines the distribution of driving torque among the motor generators. The driving torque distribution in a low output area and the driving torque distribution in a high output area are controlled using different patterns, and that which maximizes the efficiency of the motor generators overall is adopted (see, for example, Patent Document 4).
A fifth technology determines based on the total driving torque required of the left and the right front wheels and the rotational speed of the motor generators, the driving torque distribution between the left-front wheel and the right-front wheel such that the driving efficiency of the motor generators overall is maximized. The fifth technology further determines the driving torque distribution between the right-front wheel and left-front wheel such that only one of the motor generators is driven, according to the turning direction (see, for example, Patent Document 5).
A sixth technology enables selection between wheel torque distribution control that is based on energy efficiency (control of energy efficiency) and wheel torque distribution control that is based on the distribution of load at each wheel (control of load distribution) (see, for example, Patent Document 6).
Such control that uses the required torque and energy efficiency as parameters to make the energy efficiency relatively high when driving the front and the rear wheels of 4-wheel drive vehicles by an electric motor, is a known technique, as disclosed in, for example, Patent Document 2. Further, distribution ratios of load at the front wheels and at the rear wheels, for example, are obtained from the height of the center of mass of the 4-wheel drive vehicle, the distance from the center of mass to the front wheel, the distance between the front wheel axel and the rear wheel axel (wheel base), the width of the left and right tires (tread), the angular acceleration (horizontal acceleration) of the vehicle, acceleration of the vehicle in forward and backward directions, etc. and distribution ratios of load at the front wheels and at the rear wheels are caused to coincide with the distribution of load between the front wheels and the rear wheel, whereby the distribution of torque at the front wheels and the rear wheels is determined. Control that uses these parameters to obtain load distribution ratios for the front wheels and the rear wheels and that determines torque distribution ratios according to the load distribution ratios is a known technology as exemplified by, for example, Patent Document 7.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2006-180657    Patent Document 2: Japanese Laid-Open Patent Publication No. 2006-345677    Patent Document 3: Japanese Laid-Open Patent Publication No. 2007-37217    Patent Document 4: Japanese Laid-Open Patent Publication No. 2007-313982    Patent Document 5: Published Japanese-Translation of PCT Application, Publication No. 2007/064025    Patent Document 6: Japanese Laid-Open Patent Publication No. 2009-159682    Patent Document 7: Japanese Laid-Open Patent Publication No. 2006-213130